News

Nature Energy Published WNLO Research on Solar Cells with a ZnO Buffer Layer

April 10, 2017

On March 27th, the new findings by Professor Tang Jiang’s research group of Wuhan National Lab of Optoelectronics appeared on-line in Nature Energy, The related title on Nature Energy is “Stable 6%-efficient Sb2Se3 solar cells with a ZnO buffer layer”.

A new wave of new energy has been set up in the world in the context of energy crisis and environment pressure, while the solar energy takes the first place in the research field. The solar cell with a ZnO buffer layer has the merits of low production cost, weak light, light weight good flexibility, and excellent power generation performance in high temperature. Comparing with the silicon-based solar cell, it has a competitive advantage in photovoltaic building integration and mobile power supply. Currently the most successful solar cells with buffer layer on the market are cadmium telluride (CdTe) batteries, but Cd is highly toxic and Te is scarce.

Professor Tang Jiang’s research group has been focused on the new type of the solar cells with Sb2Se3 buffer layer all the time. The research group has published papers in Advanced Energy Materials, ACS Applied Materials and Interface, Applied Physics Letters, Progress in Photovoltaics and Nature Photonics. The study shows, Sb2Se3 boasts primary merits as CdTe like simple preparation, excellent optical properties and other core advantages, but the abundance of antimony selenide itself is non-toxic and elements. Thus, it embraces a brilliant future to become the "green CdTe".

The research adopted the spray pyrolysis method with zinc nitrate aqueous solution rather than the previous CDs (CdS) as the solar cell with an antimony selenide buffer layer so as to make the Zinc Oxide Research (ZnO). The material itself and preparation method are green and economic. The antimony selenide is one-dimensional material, namely (Sb4Se6) n molecular chain accumulated in two directions by Vander Ed Ley, which is similar to the crystallization of one dimensional polymer, so buffer layer’s orientation is very important and has great influence on the performance of the device.

The experimental results show, the random orientated Zinc oxide can induce the [221] the oriented antimony selenide buffer layer, while the [001] oriented Zinc Oxide induces the [120] oriented antimony selenide buffer layer. The basement and the antimony selenide buffer layer are highly correlated. The analysis of the interface atom model shows that the randomly oriented Zinc Oxide is available to more (100) surfaces, which is beneficial to the orientation induction.by bonding the subsequent growing CdSe and reducing the total energy of the interface. The defects of such interface are fewer and the recombination loss is reduced, which can be proved by the spectrum of external quantum efficiency and the open circuit voltage test.

By optimizing the buffer layer processing with Zinc Oxide and antimony selenide back field processing, the researchers finally made the solar cell with a antimony selenide buffer layer of FTO/ZnO/Sb2Se3/Au. The photoelectric conversion efficiency of FTO/ZnO/Sb2Se3/Au reaches 5.93%. This solar cell has been certificated by the Newport. More importantly, the prepared solar cells show excellent stability in packaging conditions, and can endure the double 85 (temperature 85 C, humidity 85%), maximum power point, strong ultraviolet radiation, heat shock and other critical stability test. It can basically meet the IEC61646 standard for solar cell industrial application. Compared with the cadmium sulfide buffer layer, the stability of the Zinc Oxide buffer layer is obviously improved, and the reasons are as following: First principle calculation shows that energy diffusion of Zn atoms in antimony selenide is greater than Cd. The spatial element distribution results under HADDF-STEM show that the energy diffusion of Cd in Antimony selenide approaches 50nm and Zn is barely measurable. Therefore, the interfacial diffusion of ZnO/Sb2Se3 is low but stable. The open circuit voltage decay test of monochromatic light also shows that the Zinc Oxide absorbs little light, and the damage caused by the photo-generated hole on the antimony selenide is inhibited. The study represents a new idea and new method of one-dimensional material orientation control, and a preliminary solution for the three key factors of solar cell application among the four ones (efficiency, stability, low cost and llittle toxicity), It is a great progress.

After the article was published, the fellow of MRS and APS, Dr. Supratik Guha of Argonne National Laboratory in the United States wrote an article-" Buffer against degradation" on the news &views, and commented that “The reduced toxicity and improved stability shown by Tang and colleagues are significant milestones”.

Doctor Wang Liang, Li Kanghua and Chen Chao, and postdoctor Li Dengbing are the first authors of the paper, Professor Tang Jiang is the corresponding author of the paper. This research was supported by the National Key Research and Development Plan, the Key Research and Development Plan of the Fund Committee and the Project Funding for Excellent Youth. The study has also received support and help from associate professor Li Luying, associate research fellow Niu Guangda, professor Huang Feng of Zhongshan University, Song Haisheng, deputy director of Wuhan National Lab of Optoelectronics, and Deng Huixiong, associate professor of Institute of semiconductors, Chinese Academy of Sciences,